Perfluoroalkyl-substituted compounds are used to impart oil and grease repellency to textile and paper substrates. A stain or leak proof barrier is especially desirable for paper used in many food-packaging applications.
Most commercially available fluorinated polymers useful as treating agents for imparting repellency to substrates contain predominately eight or more carbons in the perfluoroalkyl chain to provide the desired repellency properties. Honda et al., in Macromolecules, 2005, 38, 5699-5705 show that for perfluoroalkyl chains of 8 carbons or greater, orientation of the perfluoroalkyl groups is maintained in a parallel configuration, while reorientation occurs for such chains having 6 carbon atoms or less. Such reorientation decreases surface properties such as receding contact angle. Thus, shorter chain perfluoroalkyls have traditionally not been successful commercially.
Raynolds in U.S. Pat. No. 4,147,851 disclosed imparting oil and water repellency to fabric and paper by treatment with copolymers comprising (i) units derived from a perfluoroaliphatic acrylate or methacrylate monomer, and (ii) units derived from a dialkylaminoalkyl acrylate or methacrylate, or the corresponding acrylamide or methacrylamide monomer in its amine salt, quaternary ammonium or amine oxide form.
Fitzgerald et al., in U.S. Pat. No. 5,919,527, described another copolymer for treating hard surfaces comprising (i) units derived from a perfluoroalkylalkyl acrylate or methacrylate, monomers, and (ii) units derived from a dialkylaminoalkyl acrylate or methacrylate, or the corresponding acrylamide or methacrylamide monomer in its amine salt, quaternary ammonium or amine oxide form. Optionally, units derived from additional monomers were included selected from the monomer group consisting of glycidyl(meth)acrylate, blocked isocyanatoalkyl(meth)acrylate, acrylamide, vinylidene chloride, (meth)acrylic acid, sulfatoalkyl(meth)acrylate, polyoxyethylene (meth)acrylate, styrene and vinyl toluene. The above copolymers were used to provide oil, water, and stain repellency to hard surface materials used primarily for building or construction purposes such as brick, stone, concrete, tile, glass, plaster, and similar materials. There is no disclosure that such compositions are suitable for use on paper.
It is desirable to improve the method of providing oil and water repellency to paper through use of fluorochemical copolymers which do not require the use of monomers which may create difficult to remove residual toxic by-products. It is also desirable to provide copolymers useful in providing oil repellency and grease repellency to paper having perfluorinated chains of eight carbon atoms or less, thus using lower amounts of expensive fluorine, without adversely affecting the repellency performance. The present invention provides such a copolymer, a process for its preparation, and a method of treating paper for repellency.